The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Internal combustion engines include intake and exhaust valves that can be actuated by cam lobes of at least one camshaft. In some configurations the camshafts are constructed with sliding camshaft assemblies having multiple steps for varying the lift distance of an engine valve. For example, a two-step sliding camshaft may include a high lift cam lobe position for lifting an engine valve to a maximum distance, and a low lift cam lobe position for lifting the engine valve below the maximum lift distance.
At least one sliding camshaft actuator is fixed on an internal combustion engine for changing position between the multiple cam lobes. Particularly, at least one actuator pin of a camshaft actuator is operative to selectively engage displacement grooves configured on the periphery of camshaft barrels formed on the sliding camshaft assembly. As the camshaft assembly rotates, an actuator pin is selected to move into a displacement groove of the camshaft barrel which causes the sliding camshaft assembly to shift into a different position along the camshaft axis. When a sliding camshaft shifts position, the intake and/or exhaust valves are actuated differently in accordance with the changed cam lobe position, e.g., a sliding camshaft may move from a high lift cam lobe position to a low lift cam lobe position, which in turn will cause the engine operation to be different.
Thus, the sliding camshaft actuator is an important component in the proper operation of a VVL sliding camshaft system. When the actuator is cool, the pins can move more slowly than the time to move the pin into the shifting groove. When this actuator is cold, and we command the actuator on longer to move the pin because it moves slower, the coil will start to warm up and the copper loses will cause the resistance to increase and the force to push the pin out will be less. This increased electrical resistance may result in sluggish engine performance until the actuator coils warm up which, for some, could be enough of an annoyance to prompt them to seek service and/or result in unfavorable product performance ratings. Thus, there is a need for a means of eliminating the negative performance characteristics of sliding camshaft actuators after ignition in cold environments.